The Russian electoral commission was yesterday struggling to defuse a scandal over its decision to bar the strongest liberal opposition party, Yabloko, from the coming parliamentary elections, owing to a red-tape technicality.

The decision to exclude the reformist party drew protests from the Prime Minister, Viktor Chernomyrdin, who condemned it as "ill-considered and harmful", and from Communists who predicted it was the forerunner in a Kremlin-inspired scheme to cancel the December elections.

The deputy chairman of the commission, Alexander Ivanchenko, suggested it might backtrack, saying Yabloko's chances of registration were "not hopeless". It would reconsider the ban if ordered to by the Supreme Court.

Even if it changes its mind, this will not eradicate suspicion that the ban was a plot to destroy one of the most influential groups of liberal reformers. The commission, although nominally independent, is appointed by President Boris Yeltsin and is seen as a tool of the government. Yabloko is led by the economist Grigory Yavlinsky, who is planning to run for the presidency next June, and is one of the country's more popular politicians.

The commission said it had rejected Yabloko's registration for the elections to the State Duma, or lower house, on 17 December because it had dropped six candidates from the party list without providing proof of their consent, a minor breach of election law.

The chief proponent of the theory that the ban is a conspiracy is Mr Yavlinsky himself, who accused Kremlin hawks of using Mr Yeltsin's illness to sabotage his presidential bid. "This is the beginning of the preparations for the presidential challenge," he said.

Others said if it was an act of skulduggery, it was ill-judged. With Russians in a nationalist mood - polls show they are leaning strongly towards the Communist and nationalist parties - Mr Yavlinsky is not a particularly promising presidential candidate. Banning his party from the parliamentary elections is only likely to boost his popularity. "This has given him and his party something which most Russian politicians covet, the air of having been persecuted," said Dimitri Trenin, of the Carnegie Endowment for International Peace in Moscow.

A more plausible theory is that Yabloko, which means "apple", and is an acronym of its three founders' names, was the victim of petty bureaucracy, and of a clash between the commission's chairman, Nikolai Ryabov, and Mr Yavlinksky. Both men have a reputation for arrogance. Mr Ryabov has accused the Yabloko leader of being "high and mighty".

The Yabloko scandal is further adding to the nation's jitters, which began when Mr Yeltsin was taken to hospital on Thursday. He remains isolated from the outside world and is still not receiving visitors.